240 SPECIAL BRONZES on a sand-bath with 3-4 c.c. of cone, sulphuric acid until white fumes of sulphuric acid appear. The lead is determined as sulphate in the way given for the gravimetric analysis of ordinary brasses. 3. Determination of the Copper, Iron, Nickel and Zinc.—(«) ELECTROLYTICALLY. The liquid freed from lead is evaporated until the alcohol is expelled and the residual liquid mixed with 20 c.c. of nitric acid and electrolysed as in the case of argentan. (6) GRAVIMETRICALLY. The liquid freed from lead is evaporated to eliminate the alcohol, mixed with 200-250 c.c. of water, heated to boiling and the copper precipitated with hydrogen sulphide, the subsequent pro- cedure being that described for the gravimetric analysis of argentan. 4. Determination of the Phosphorus, Arsenic and Sulphur.— See Ordinary Bronzes. * * * Lead-rdckel-bronzes have the following mean composition : 64% Cu, 30% Pb, 5% Sn, and i% Ni. Aluminium -bronzes Aluminium-bronzes have a fine, golden-yellow colour and are used for making vases, ornamental articles, etc. They consist essentially of copper and aluminium (3-10%) and often contain small quantities of silicon and iron. Their analysis includes : 1. Determination of the Silicon.—I gram of the alloy is heated gently with 10 c.c. of nitric acid (D 1-2) and the solution evaporated with 10 c.c. of 50% sulphuric acid until white fumes of sulphuric acid appear. The residual liquid is mixed with 30 c.c. of water, heated for some time and, when cold, filtered through a small filter ; the residue of more or less pure silica is washed, dried, calcined in a platinum crucible and weighed. It is then treated with hydrofluoric acid, etc., as in the determination of silicon in iron. 2. Determination of the Copper.—The filtrate is treated with 4-5 c.c. of nitric acid, diluted to about 150 c.c. and subjected to electrolysis (see Electrolytic Determination of Copper in Ordinary Brasses). 3. Determination of the Iron and Aluminium.—After removal of the copper, the liquid is rendered alkaline with ammonia, boiled for some time and the precipitated aluminium and ferric hydroxides filtered off, washed, calcined and weighed. The oxides are then fused with potassium bisulphate, the residue taken up in dilute sulphuric acid and the iron in the solution determined electrolytically or volumetrically. The iron and aluminium are thus obtained separately. * * * The compositions of the more important industrial types of aluminium- bronzes are as follows (Guillet) :rus.